Alert archive / Illinois / Mesoscale Discussions in 2023

Mesoscale Discussion 1639

July 20, 202310 counties in Illinois; 4 counties in Missouri

The Storm Prediction Center issued this mesoscale discussion at Jul 20, 2023, 8:58 AM CDT for 10 counties in Illinois; 4 counties in Missouri. It was in force for 92 min.

The area

The outline as issued.

The facts

Issued: Jul 20, 2023, 8:58 AM CDT (13:58 UTC)
Expired: Jul 20, 2023, 10:30 AM CDT
In force: 92 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

Counties Bond County, IL, Christian County, IL, Clinton County, IL, Jersey County, IL, Macoupin County, IL, Madison County, IL, Monroe County, IL, Montgomery County, IL, Saint Clair County, IL, Sangamon County, IL, City of Saint Louis, MO, Franklin County, MO, Jefferson County, MO, Saint Louis County, MO

The radar

The St Louis radar (KLSX), 36 km from the middle of the area, began a volume at 13:57 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 2.0 hours before the alert went out and 206 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1586 J/kg
Mixed-layer CIN: -43 J/kg
Mixed-layer LCL: 680 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 50 m²/s²
0-3 km storm-relative helicity: 66 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.2

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 7:47 AM CDT	Mesoscale Discussion	SPC	Alexander, Massac, Pulaski	118 min
Jul 20, 1:15 PM CDT	Mesoscale Discussion	SPC	Vermilion	90 min
Jul 20, 1:45 PM CDT	Severe Thunderstorm Watch	SPC	Champaign, Clark, Coles, Cumberland, Douglas, Edgar and 1 more	8 hr
Jul 20, 11:51 AM CDT	Mesoscale Discussion	SPC	Pemiscot	84 min

Nearby

Mesoscale Discussions in Illinois, 2023 Mesoscale Discussions in Missouri, 2023 Every mesoscale discussion in 2023

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.